I am the author of Toe Tags and Tequila and I think BookCrossing.com is a great way to get the word out. I read somewhere that the author of The Girl With The Dragon Tattoo released wild copies of his book to help kick off sales.
In that same spirit, I am releasing 100 copies of my book before it is even available at Barns&Noble, Amazon.com, etc. I am sending out 3 copies today with friends that are traveling back to the UK. I dropped three others last week (on a ship, at a doctor's office, and in a hotel room).
I don't know if it will really help but I can't think of a better or more exciting way to advertise. By the end of the month, all 100 will be released. Then I get to see where they go - I will see what adventures they have.
After posting this note - I saw that I had actually posted last year. Since then I had to change publishers due to release date delays. Toe Tags and Tequila is now set to be release in book stores May 7, 2013. I thought BookCrossing.com was a good idea then and now.